<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>my img</title>
    <style>
        .c1 {
            width: 500px;
            border: 1px black solid;
        }
        img {
            width: 100%;
            visibility: hidden;
        }
        .c1:hover img {  /*鼠标悬停在c1 class上时img的样式*/
            visibility: visible;
        }
        html {
            font-size: 16px;
        }
        .c2 {
            font-size: 2rem;
            /*color: purple;*/
            /*color: rgb(100, 100, 100);*/
            color: #140650;
        }
        .c3 {
            font-size: 2em;
        }
    </style>
</head>
<body>
<div class="c2">
    父元素
    <div class="c3">
        子元素
    </div>
</div>


<div class="c1">
    <img src="http://pic1.win4000.com/wallpaper/0/58f5dfe62b563.jpg">
</div>
</body>
</html>